Use of a catheter to deliver a therapeutic agent to the brain (e.g., into the intracerebroventricular (ICV), intrathecal, or intraparenchymal (IPA) space) generally involves the insertion of the catheter into the cranial cavity via a burr hole. The catheter may be inserted until a therapy delivering catheter tip is positioned at a predetermined target site, after which the therapeutic agent may be dispensed through the catheter in accordance with a desired therapy profile.
During a typical implantation procedure, an incision is made in the scalp to expose the patient's skull. After forming the burr hole through the skull, the catheter may be inserted into the brain. To accurately place the catheter, clinicians may use stereotactic apparatus/procedures in a process referred to as framed stereotaxy. In framed stereotaxy, a ring-like frame is mounted to the patient's skull by pins or screws. The ring-like frame is then used to determine a three-dimensional data set, from which coordinates for the target site may be calculated. Various components and instruments may be utilized with the stereotactic apparatus to assist in guiding the catheter tip to the target site.
Depending on the stiffness of the catheter, a stylet may be utilized to permit the clinician to adequately push the catheter into the body. Typically, a stylet is constructed as a slender rod of relatively stiff but flexible material. The stylet may be inserted into a proximal end of the catheter until it abuts or otherwise contacts an engagement surface within the catheter near the catheter's distal end. The stylet may then be used to push the catheter until the distal end of the catheter is at the desired target site.
Once the catheter tip is implanted at the target site, the stylet may be withdrawn from a proximal end of the catheter (i.e., the end that remains outside of the skull). The catheter may then be anchored relative to the burr hole, e.g., via a burr hole anchor surgically attached to the skull. An end of the protruding portion of the catheter may then be connected, often via a secondary catheter, to a reservoir containing the therapeutic agent. After the secondary catheter is connected and tunneled beneath the skin to the reservoir, the scalp incision(s) may be closed and the system may deliver therapy in accordance with the desired profile.
To provide the desired stylet rigidity, an outer diameter of the stylet may be sized to fit tightly within the catheter. As one can appreciate, extraction of such a stylet may result in unintended pulling or displacement of the catheter, and therefore movement of the catheter's therapy-delivering tip, from its desired location (such displacement may be caused by a variety of factors including, for example, frictional and/or suction forces between the stylet and catheter, both of which may be amplified by the use of a relatively soft catheter material). Stated alternatively, the process of physically extracting the stylet from the catheter may inadvertently (e.g., via frictional interaction with the catheter) impart forces that are capable of displacing the catheter tip relative to the target site. Depending on the application, even slight displacement of the tip may result in reduced therapeutic efficacy.
Moreover, in some applications, the stylet may be attached to various structure, e.g., to part of the stereotactic frame, to hold the stylet stationary and/or to assist with its insertion into and/or removal from the catheter. Depending on the construction and material of the stylet, such attachment may present problems. For example, where a set screw or the like is used to contact and restrain the stylet, inherent variability in clinician actuation of the set screw may result in under- or over-tightening of the set screw, the former potentially resulting in inadequate anchoring, while the latter may potentially damage the stylet.